The invention relates to a surface coating for end products, which is formed from a mixture of metals wherein Group 1 contains at least titanium, zirconium, hafnium or vanadium, and Group 2 contains at least aluminum or silicon, and this metal mixture is applied to the end product by the vacuum method, especially in a reactive nitrogen atmosphere.
It is already known to use compounds such as TiN, TiC, and Al.sub.2 O.sub.3 for the coating of cutting and shaping tools to reduce wear (reprint from issue 7,42, volume 1988, Metall Verlag Berlin). Other applications are in diffusion barriers in microelectronics, first-wall coatings in fusion apparatus, or possible use in superconductivity technology. The hard substances are required to have very different properties according to the various technical applications. By far the greatest application at this time is in the reduction of wear in cutting and shaping tools and in decorative coating, wherein the ability of the tools to withstand wear is improved by the coating.
The most frequently studied coating materials are the "binary" nitrides and carbides, TiN and TiC. In a series of tests mixtures of other transition metals are being treated, mainly ZrN and HfN, but also CrN, NbN, and others. Early on, the "ternary" metal mixture Ti(C.sub.x N.sub.1-x) which has a gradual transition of properties from one to the other hard substance, aroused interest on account of the complete miscibility of the TiC--TiN system.
Heretofore TiAl--N.sub.x coatings have been produced only by processes of physical gas-phase deposition (PVD--physical vapor deposition), mainly by reactive magnetron sputtering in direct-current and HF operation with a single and double cathode arrangement, but also by the reactive arc evaporation process and triode-ion plating. According to the apparatus used and the chosen process conditions, very different coatings were obtained. Particularly influential deposition parameters have proven to be the partial pressure or gas flow for nitrogen (reactive gas) in proportion to the argon (sputtering gas), as well as the negative substrate bias and the plasma density in the vicinity of the substrate by which an ion bombardment of the substrate is achieved during the deposition.
As targets for magnetron sputtering, both mechanically made targets with a drop of aluminum inserted in a titanium target, but preferably TiAl targets made by powder metallurgy, found application.
High-speed steel, tool steels and stainless steels of various types, as well as hard-metal and stellite (cutter inserts) were used as substrate materials. These materials are the common materials for cutting and shaping tools and components.
It is furthermore known from U.S. Pat. No. 4,337,300 (DE 30 30 149 C2) to provide an intermediate layer between the base body and the metal coating in the case of cutter inserts and cutting tools of high-performance high-speed steel or hard-metal. The known intermediate layer consists here of vapor-deposited titanium, and the wear-resistant layer of a titanium-metal mixture from the group, titanium carbide, titanium nitride, titanium carbonitride, titanium oxycarbide and titanium oxycarbonitride deposited from a vapor, the thickness of the intermediate layer not exceeding 0.9 .mu.m and the wear-resistant layer being 0.5 to 10 .mu.m thick. The hard layers crumble easily on account of their high internal tension; also, disadvantages are to be expected in the use of the tool due to the "soft" intermediate layer.
U.S. Pat. No. 3,895,156 discloses the application of hard-substance layers such that layers of pure hard substances and layers of metals alternate. It has been found, however, that the hard layers disposed on soft intermediate layers are very sensitive to point stress and tend to break up on account of the flexibility of the soft layer.
Furthermore, the problem still exists that thick layers have high internal tensions, so that in functional parts which are subjected to great stress in their use the coatings are easily broken off or spall, and the functional parts are no longer usable after a short period of time.
In the production of hard-substance layers of metals of Group IVa of the Periodic Table including Ti, it is also taught by European Patent 0,121,625 B1, to which U.S. Pat. No. 4,428,812 corresponds, to operate with a pulsating feed of nitrogen order to avoid the reduction of the rate of deposition which otherwise occurs in the continuous feeding of reactive gas. The alteration of the gas feed in this known process takes place with such great frequency that it leads to no recognizable change in the layer structure, and instead only homogeneous layers are thereby formed.
In all of the layers known heretofore having a very hard surface an additional problem has been that these layers have a relatively high coefficient of friction, which likewise led to high layer stresses.